The so-called Temple of Portumnus is in the extreme east part of the city, near a main gate in the city wall (20). It was a round building with a diameter of c. 19 meters, of which an enormous stump of masonry has been preserved. It is made of opus latericium. The structure has been dated to the Severan period.
The interior of the Temple of Portumnus. Photo: Boscolo 2021.
The exterior of the Temple of Portumnus. Photo: Jan Theo Bakker.
Detail of the exterior of the Temple of Portumnus. Photo: Jan Theo Bakker.The lower part of the building is a platform with two cross-shaped corridors with niches, covered by cross-vaults, and with a round corridor along the perimeter. It had two entrances and was not connected with the upper part. The upper part consists of a single room that was covered by a cupola, possibly with an oculus as in the Pantheon. In the interior are huge rectangular and semicircular niches, with eight columns in between. The lower part of the walls was decorated with marble, the upper part with paintings imitating marble and stucco reliefs. The exterior was decorated with 24 marble columns.
The building according to Luigi Canina (1830), as reproduced in Testaguzza 1970, p. 217.
Plan of lower part (top left) and upper part. Reconstruction of the exterior (top right) and section.
Left: the building according to Giuliano da Sangallo (1830). Right: according to Giovanni Batista Montano (between 1582 and 1621).
Image: Boscolo 2021, fig. 3.The function of the building is not clear. In the past it has been suggested that it was a temple dedicated to the harbour deity Portumnus and to Fortuna Tranquilla. This was deduced from three inscriptions that are today regarded as forgeries (CIL XIV, 16*, 17*, 18*). This of course does not mean that the building could not have been a temple. It has also been suggested that it was a mausoleum. But of who? The Severan Emperors were buried in mausolea in Rome. It is furthermore interesting to note that the building is located at the precise point where the arches of an aqueduct (to the east) end, and where the aqueduct continues underground (to the west). Could it have "celebrated" the arrival of the aqueduct?
The building is in the area enclosed by the city wall from late antiquity. The roughly triangular shape of the city wall here (19, 22) suggests that this was deemed important.
The interior of the Temple of Portumnus in 1896. Photo: British School in Rome.
